The Study And Application On On-line Pre-concentration Technology In Non-aqueous Capillary Electrophoresis

Since1980, capillary electrophoresis (CE) has quickly developed into one of themost efficient separation techniques[1]. CE offers several distinct advantages over otherseparation methods: very small sample volume，highspeed，highefficiency, and widelyapplied in routine analysis. Nonaqueous capillary electrophoresis (NACE) is theapplication of a conductive electrolyte dissolved in either one organic solvent or amixture of several organic solvents. Organic solvents proved to be useful for the analysisof hydrophobic compounds, which are difficult to separate with aqueous buffers. Basedon the previous literatures, this article reviewed the development and application onpharmaceutical, food and environment analysis by NACE. The techniques ofcombination Sweeping-micellar electrokinetic chromatography (MEKC), field amplifiedsample injection (FASI) and ultra high conductivity zone (UHCZ) were explored andachieved. The content is described as five chapters:1. A review provides a comprehensive overview at NACE technique. Specialattentionis given to theoretical, methodological, and technical challenges and theachievements of capillary electrophoresis in nonaqueous media were demonstrated.2. A new sweeping-micellar electrokinetic chromatographic (sweeping-MEKC) wasused for the simultaneous separation and determination of fumalic acid, caffeic acid andprotocatechuic acid in honeysuckle mixture. The result indicated that a best separation ofthe three organic acids were obtained on a uncoated fused silica capillary column (55cm×50μm i. d., effective length36cm) by using the background electrolyte containing20mmol/L NaH2PO4,80mmol/L SDS and12.5%(by volume) acetonitrile at pH2.20.Under the optimum conditions, the separation of the three organic acids was performedwithin20minutes. The calibration curves showed good linearity(μg/mL) in the range of2.30～36.80for fumalic acid,1.82～29.12for caffeic acid and1.10～17.64forprotocatechuic acid with detection limits of98.52μg/L,118.73μg/L,27.27μg/L,respectively. The spiked recoveries were93.92%～101%,95.98%～104.04%,93.91%～102.7%.3. A NACE-FASI method was developed for simultaneous assay of sophoridine,matrine and oxymatrine in sophora flavescens. The result indicated that a best separationof the three alkaloids were obtained on a uncoated fused silica capillary column (55cm×50μm i. d., effective length34cm) by using the background electrolyte containing50mmol/L ammonium acetate,20%acetonitrile(by volume),0.75%acetic acid(byvolume). Under the optimum conditions, the separation of the three kaloids wereperformed within15minutes. The calibration curves showed good linearity(10-2μg/mL)in the range of5.94～95.4for sophoridine,11.04～176.64for matrine and17.76～284.16for oxymatrine with detection limits of2.02μg/L,1.32μg/L and1.01μg/L,respectively. The spiked recoveries were96.66%～101.55%,94.02%～100.53%and 100.37%～102.74%, respectively.4. A new FASI-MEKC method was used for the simultaneous separation anddetermination of emodin, cinnamic acid, ferulic acid and isoferulic acid in rhizomacimicifugae. The result indicated that a best separation of the four materials wereobtained on a uncoated fused silica capillary column (50cm×50μm i. d., effective length38cm) by using the background electrolyte containing70mmol/L Na2B4O7,4mmol/LNaOH,5mmol/L CTAB and10%acetonitrile(by volume). The separation voltage was-22kV, sample injection voltage was-22kV and injection time was6s, injection time ofwater was10s. Under the optimum conditions, the four materials were performed within20minutes. The calibration curves showed good linearity(μg/L) in the range of8.8～140for emodin,9～144for cinnamic acid,16.8～269for ferulic acid and8.1～129forisoferulic acid with detection limits of253ng/L,190ng/L,293ng/L and389ng/L,respectively. We found this method reduced detection limits vastly, the enrichment factorof the proposed method was increased100～400times to compare with the normalMEKC method.5. A new ultra high conductivity zone-low temperature zone(UHCZ-LTZ/Sweeping)-MEKC chromatography method was used for the simultaneousseparation and determination of benzoic acid, sorbic acid and dehydroacetic acid in food.The result indicated that a best separation of the three preservatives were obtained on auncoated fused silica capillary column (50cm×50μm i. d., effective length36cm) byusing the background electrolyte containing60mmol/L CH3COONH4,6mmol/L NaOH,6mmol/L CTAB and10%acetonitrile(by volume). The separation voltage was-22kV,sample injection voltage was-20kV and injection time was8s, injection time ofhigh-conductivity zone was15s. Under the optimum conditions, the three preservativeswere performed within20minutes. The calibration curves showed good linearity(μg/L)in the range of14～224for benzoic acid,12.5～200for sorbic acid, and29.3～468fordehydroacetic acid with detection limits of610ng/L,361ng/L and999ng/L,respectively.